BARI will consist of a prospective randomized trial designed to compare the long-term efficacy of PTCA and CABG in clinical subsets of patients with multivessel coronary disease and severe angina, unstable angina or angina after acute MI, and a registry of all patients undergoing coronary angiography because of severe or unstable angina, with or without MI, at 12 participating clinical sites. Roughly 1,800 patients will be randomized to PTCA or CABG during the 24-month recruitment period and duration of follow-up will be a minimum of four years. Clinical and objective data will be collected for each subject in the registry and in the randomized trial at entry and during follow-up. The best choice of therapy is unclear at present for these large subsets of patients with severe coronary artery disease and the randomized trial should establish the relative merits of PTCA and CABG, namely the safety and rate of success of each procedure, recurrence rate of angina, need for re-intervention and occurrence of late coronary events, and help to determine which procedure should be applied first. The registry data will, among several objectives, assess the validity of extending the conclusions of the trial to a larger population of patients with severe angina and multivessel coronary disease.